Electronic Ink Tattoos

Electronic ink is ink the pixels of which that can be turned "on" or "off" using an electric field. It's implemented at least two ways, either using electrically charged balls of ink, background colored on one hemisphere and ink colored on the other, or using capsules containing a suspending liquid and ink and background particles, with each type of particle having an opposite electric charge. Application of an electric charge either rotates the ink ball (in the first implementation), or attracts/repels the appropriate type of particles (in the second implementation), to turn the ink on or off. (see: below for explanation of technology, thanks for fixing the ref, Aristotle.)

Using the second implementation, inject the capsules in place of tattoo ink. The tattoed person can use a handheld electric field generator to alter the tattoo to taste.

(In case you wonder, I don't have tattoos. My body's already too distracting.)